Software for Syncing files between storages (Linux)

So I recently quitted Google Drive and downloaded all my data and hoping to keep it on Hard drives myself, They are external plug in types and I want the files synced like it was on my computer. So when I plug it in it copies/syncs the things on my computer, anyone knows somethign like that?

Syncthing is the closest to what you want.

That only works from PC to PC (it was my first thought too).